1. Field of the Invention
The present invention relates to an automatic control for a platen heater and more particularly to automatic control for regulating the platen heat in a lid applying apparatus.
2. Background and Prior Art
It is well known in the container art to apply foil caps on containers by use of a platen heater which seals the foil to the container. The platen is used to activate a hot melt, in the form of glue or shellac or the like, onto the side of the container. Proper sealing can only be accomplished when the hot melt is triggered at a high enough temperature and absorbs enough heat to effect the proper seal. In that regard, there is a time and temperature correlation which is necessary in order to be certain that the seal is effective to prevent the container contents from leaking, spilling, spoiling, etc.
Two conditions must be ensured in order to be certain an adequate seal has been effected. Temperature of the heater platen must be high enough and the foil must experience the heater platen temperature for a sufficiently long period of time to absorb enough heat energy. The time during which the foil cap is in contact with the heater platen is hereinafter referred to as the dwell time.
In prior art container manufacturing devices, such as that disclosed in Reissue Pat. No. 29,448, the disclosure of which is hereby incorporated by reference after a container was assembled and filled in various rotating stations, it would pass through a cap application station. Automatic container forming and filling devices such as that disclosed in the above-referenced patent are capable of producing 350 or more containers per minute. When operating at a low speed, the heater platen could be operated at a temperature which was just sufficient to activate the hot melt, for example, 240.degree. to 280.degree. F. That is because at low speeds, the foil could absorb enough heat from the platen to effect a good seal. As the speed of production increases, in order to ensure that the heater platen would transfer enough heat to the foil cap, its temperature must be increased since the dwell time of each foil cap on the platen is significantly less. Therefore, as the speed of production of the machine is increased, it is also necessary to increase the temperature of the platen correspondingly in order to ensure proper sealing. Unfortunately, it is all too common for machine operators to increase the rate of production of the machine without appropriately adjusting the temperature of the heater platen thereby producing defectively sealed containers.
In addition, in the prior art equipment, when the sealing station is shut down, for example during a lunch break, the heater platen temperature tends to decrease towards ambient. After the machine is restarted, owing to the significant thermal inertia of the platen, it ordinarily takes up to 15 minutes before the platen becomes hot enough to again produce properly sealed container caps. If production is recommenced before the platen temperature is adequate to activate the hot melt on the foil, the initial machine production may all have defectively sealed caps. In a fast operating machine, this could mean that literally thousands of containers filled with merchandise are defectively sealed.